1. Field of the Invention
This invention is related generally to a method and apparatus for recycling building materials in a cement kiln as a supplemental fuel source and source of raw material for the cement.
2. Prior Art
Cement is produced by heating raw materials, forming a closely controlled chemical combination of calcium, silicon, aluminum, iron and small amounts of other ingredients. Common among the materials used in its manufacture are inorganic materials, such as limestone, shells, and chalk or marl combined with shale, clay, slate or blast furnace slag, silica sand, and iron ore. Lime and silica typically make up about 85% of the mass. The raw materials are heated in a cement kiln at high temperatures of typically 2600xc2x0 F. to 3000xc2x0 F. (1430xc2x0 C. to 1650xc2x0 C.). The inorganic minerals are xe2x80x9cdigestedxe2x80x9d in the kiln through a very complex set of chemical reactions, yielding oxides, and then finally complex silicates, which comprise the clinker. At 2700xc2x0 F. (1480xc2x0 C.), this series of chemical reactions cause the materials to fuse and create cement clinker-grayish-black pellets, often the size of marbles. Clinker is discharged red-hot from the lower end of the kiln in marble-sized pieces, and is transferred to various types of coolers to lower the clinker to handling temperatures. Cooled clinker is combined with gypsum and ground into a fine gray powder. The clinker is ground so fine that nearly all of it passes through a No. 200 mesh (75 micron) sieve. This fine gray powder is portland cement.
The raw materials are placed in the high end and as the kiln rotates the materials move slowly toward the lower end. Flame jets located at the lower end of the kiln heat the materials in the kiln. The kiln heat drives off, or calcines, the chemically combined water and carbon dioxide from the raw materials and forms new compounds (tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite). Of the material that goes into the feed end of the kiln, about 67% is discharged as clinker.
As described in U.S. Pat. No. 5,454,333, pumpable and solid hazardous wastes have been used a supplemental fuel to produce the heat for heating the mixture. Such wastes are typically used primarily for the heat value thereof.
U.S. Pat. No. 5,888,256, which is incorporated herein by reference, describes a process for using various waste fuel sources, analyzing the ash of each, and adjusting the raw material inputs for the cement based on the ash composition. Such wastes are previously known wastes used in such processes, such as sludge waste and such.
U.S. Pat. No. 5,888,256, which is incorporated herein by reference, describes a process for using various waste fuel sources, analyzing the ash of each, and adjusting the raw material inputs for the cement based on the ash composition. Such wastes are previously known wastes used in such processes, such as industrial waste sludge. The ""256 patent requires a minimum of two waste streams, and blending and grinding to achieve a maximum 1000-micron particle size with a minimum BTU value and a maximum ash content. Accordingly, the ""256 patent restricts the type and form of wastes which can be used.
U.S. Pat. No. 8,833,474 describes using waste materials from electric arc furnaces to supplement the input materials for cement to provide an inexpensive raw material, but not to recover fuel value therefrom.
Asphalt shingles have been used extensively as a roofing material for the construction of buildings. In the process of making shingles, an organic or glass mat is coated with asphalt filled with limestone or dolomite, and inorganic granules are imbedded in the filled asphalt. Waste product from such an operation, or shingles removed from a house after their useful life, are sent to a landfill, due to the variety of materials used and the difficulty in separation of such materials. Often during the removal of old shingles form a house, nails used in the installation thereof, as well as rotten boards, tar paper, vents and other such materials are removed and sent with the shingles to the landfill. Furthermore, composite shingles have come into use in the recent past, an example of which is the Owens Coming Mira Vista(copyright) Shake, which comprises a filled polymeric shingle. Similar to the asphalt shingle, such a composite shingle may be recycled by combusting the polymeric material and using any filler materials therefrom as a component of the cement. Furthermore, other building materials such as siding materials, including asphalt siding, cedar siding, cementious siding and such, may be recycled in a similar manner.
It would be desirable to find an alternative disposal method for scrap building materials from the manufacturing process and building renovations, including asphalt shingles.
According to the present invention, an improved recycling process is described to recycle building materials. As such, the disposal costs and landfill space for such materials are avoided. Furthermore, the energy value of such materials is recovered, and the inorganic constituents of the shingles or recycled building materials are incorporated and become part of the minerals useful in the manufacture of cement, reducing the cost for these inputs in the manufacture of cement.
Accordingly, a method of recycling building materials is described, including the steps of introducing the building material into a cement kiln, and combusting a combustible portion of the building material as a fuel within the kiln. The noncombustible portion of the building material is incorporated into a clinker material within the kiln.